The invention relates to a connecting rod assembly for connecting high pressure pumps to mechanical or hydraulic pump drives.
The present invention relates to the connecting rod assembly for connecting high pressure pumps to mechanical or hydraulic pump drives. These pumps are of the reciprocating type and are driven by power from an outside source like a diesel engine. The power end of the connecting rod assembly includes a crankshaft which is connected to a drive rod (often called a connecting rod) which articulates the motion of the crankshaft to a crosshead.
The crosshead, like a piston, creates a linear reciprocating motion derived from the motion of the crank shaft through the drive rod. The fluid end of the connecting rod assembly imports and pressurizes the fluid before it is expelled. The reciprocating motion of the crosshead is typically applied to a plunger and the plunger compresses fluid in the fluid end of the pump during the thrust portion of the pump cycle.
In most crosshead designs there are many moving parts which are subject to wear and tear. Most crossheads utilize xe2x80x9cwrist pinsxe2x80x9d to allow oscillating motion of the drive rod relative to the crosshead about one axis only. Often, a cylindrical wrist pin bearing is employed between the wrist pin and the connecting rod to transmit reciprocating load to the crosshead.
Bearing wear accounts for most down time and repairs of fluid reciprocating pumps. Specifically, the wrist pin bearing between the connecting rod and the wrist pin becomes worn and deformed from the load transmitted during the thrust stroke of the pump when the plunger and crosshead are acting against high pressure fluid being pumped through the fluid end of the pump. As the wrist bearing wears, it creates xe2x80x9cslopxe2x80x9d between the connecting rod and the crosshead causing the pump to knock as it operates. Increasing the bearing size and surface results in longer bearing life. However, the result is an unacceptable increase in pump size and weight.
An additional problem with many bearing arrangements currently in use is misalignment of the drive rod with the crosshead. Misalignment causes the bearings to wear on one side rather than evenly. This uneven wear results in a further reduction of bearing life. A bearing arrangement which is self-aligning and will reduce uneven bearing wear is desirable.
Conventional crosshead designs are similar to pistons which reciprocate inside of a machine bore which is larger than the crosshead (See instructions, 12xe2x80x3 Stroke Type 6HHE-VE-3-3-3 Ethylene Primary Compressors Ingersoll Rand Engine Process Compressor Division/029-30961/Painted Post Division (1974). Other crosshead designs incorporate flat or large radius curved crosshead slide plates sometimes referred to as xe2x80x9cslippersxe2x80x9d (See instructions, Compressors Type F6-H230116/the Burkhardt Engineering Works Ltd./Dornacherstrasse 210 CH-4002 Basle).
A variety of connecting rod assemblies which employ crossheads are found in the prior art. None of these connecting rod assemblies employs a single centrally located drive bearing of spherical design in the crosshead, as does the instant invention. U.S. Pat. No. 5,247,873 is directed to a connecting rod assembly having a crosshead wherein a ball and socket arrangement is employed to connect the connecting rod to the crosshead. Lubrication channels criss-cross the crosshead. In most connecting rod assemblies, a wrist pin is used to connect a crosshead to a connecting rod. In the invention of this patent, a wrist pin is not necessary.
U.S. Pat. No. 5,771,694 illustrates a crosshead system for a swashplate engine. A plurality of crossheads are constrained to move in a reciprocating fashion by traveling along a pair of parallel guide rods.
U.S. Pat. No. 5,033,869 discloses a linear slider with a floating bushing, formed from a block and two parallel shafts mounted through the block. The first shaft runs on coaxial bushings, while the second shaft runs in a single floating bushing. Lubrication channels may be present so that the floating bushing and shafts may be easily lubricated.
U.S. Pat. No. 4,905,577 illustrates a hydraulically operated piston machine which includes at least one cylinder and a piston axially movably guided in the cylinder. The piston is connected to a crankshaft by means of a connecting rod. The connecting rod and the piston each have spherically-shaped bearing surfaces for connecting the connecting rod and the piston with each other in an articulated manner.
The crosshead design of the instant invention employs four bushings, preferably composed of sintered bronze, which slide on two parallel cylindrical rods, or tie rods. Each bushing is held in the crosshead via interference fit. This design is novel in that it places the contact points of the tie rod with the crosshead at the extreme outside location of the crosshead in order to minimize deviation of the crosshead""s linear motion path in operation. Minimization of the motion path deviation results in more reliable operation of the attached pump components. The crosshead design of the instant invention also demonstrates novelty in the simplicity of the of the connection between the drive rod and the crosshead. Most crossheads utilize xe2x80x9cwrist pinsxe2x80x9d to allow oscllating motion of the drive rod relative to the crosshead about one axis of rotation only. In this invention, a spherical bearing is used to connect the drive rod to the crosshead, the spherical bearing eliminates the problem of aligning the drive rod to the crosshead, since uniform clearances exist in the spherical bearing regardless of exact alignment within the range of motion of the spherical bearing. The spherical bearing allows rotation about all three coordinate axes. The spherical bearing and the four bushings are supplied lubricating oil via a flexible hose.